The cutting tool assembly of the kind to which the present invention applies comprises a tool holder formed with an insert retaining pocket and a cutting insert located therewithin so as to present an operative cutting corner and associated cutting edges. The cutting insert has a lower surface for bearing against the pocket's base wall either directly or indirectly via a correspondingly shaped and sized shim. A shim is typically prepared from a material harder than that from which a tool holder is prepared. As such, its use is preferable because it acts to absorb cutting forces, particularly the tangential component thereof, acting on an insert's operative cutting corner, thereby preventing damage to a relatively expensive tool holder. Mostly, the shim is independently secured into the retaining pocket by holding means such as split tubular pins, threaded sleeves, and the like whilst the cutting insert is secured therein by holding means such as locking screws, central locking pins, levers, wedges, clamps, and the like.
For the purpose of accurate positioning of a shim on a pocket's base wall and increasing the area of contact therebetween and with the cutting insert, it is common practice to grind the shim's upper and lower surfaces. In theory, this practice is designed to prevent the plastic deformation occurring at the front portion of a pocket's base wall supporting an insert's operative cutting corner as caused by the considerable bending moment thereon as applied by a cutting forces' tangential component. However, in practice, even the slightest deformation occurring at the front portion of a tool holder's pocket base wall leads to an unstable seating of a shim which, in turn, leads to vibrations during machining operations. As such, a shim can no longer act effectively as an absorbing cushion and the tool holder body is rendered of no further use.
It is therefore an object of the present invention to provide a new chip cutting tool assembly comprising a cutting insert and preferably a shim in which means are provided for substantially reducing or avoiding the above-referred disadvantage.